PROCESS FOR INHIBITING COLOR FORMATION IN o-NITROPHENOL

ABSTRACT

The formation of color bodies in o-nitrophenol is inhibited by treatment of the reaction mass with an alkali metal bisulfite, alkali metal metabisulfite, urea, or sulfur dioxide.

United States Patent Terpstra 51 Dec; 5, 1972 I541 PROCESS FOR INHIBITING COLOR FORMATION IN -NITROPHENQL [52] US. Cl. ..260/622 R [51] Int. Cl ..C07c 79/26 [58] Field of Search ..260/622. R, 629

r [56] References Cited UNIITEDQS'TATES PATENTS 2,576,161 11/1951 .Thomponl ..260/629 3,283,011 11/1966 Cox ..260/622R 3,506,724 4/1970 Tuemmler et a1 ..260/622 R FORElGN PATENTS OR- APPLICATIONS 479,765 2/1938 Great Britain ..2'60/622 Primary ExaminerBemard Helfin Assistant Examiner-W. B. Lone Att0rneyJ. E. Maurer, F. A. Brusok and Edward P. Grattan [5 7] ABSCT The formation of color bodies in o-nitrophenol is inhibited by treatment of the reaction mass with an alkali metal bisnlfite, alkali metal metabisulfite, urea, or sulfur dioxide.

5 Claims, No Drawings PROCESS FOR INHIBITING COLOR FORMATION IN O-NITROPHENOL This invention relates to color improvement of nitro 5 phenol. More specifically, this invention relates to a new and improved method of improving the color of o-nitrophenol by treatment, during processing, with a color inhibitor selected from the group consisting of alkali metal bisulfites, alkali metal metabisulfites, urea and sulfur dioxide.

o-Nitrophenol is manufactured commercially by hydrolysis of o-nitrochlorobenzene with I aqueous caustic followed by acidification of the resulting alkali metal o-nitrophenate with a strong mineral acid such as sulfuric acid. o-Nitrophenol is then separated from the aqueous layer with conventional techniques. Product resulting from commercial processes similar to that described above routinely contains dark colored materials that are difficultto separate from the desired product. In addition to adverse effects on yield, these dark colored materials have a deleterious effect on product quality, particularly color, which in turn discolors end products that are prepared using 0- nitrophenol. I

Color can be compared by quantitatively measuring light transmission through a 5 percent by weight solution of o-nitrophenol in acetone with a Beckman Spectronic instrument using a 1 inch cell at wavelengths of 475 to 560 millimicrons. Heretofore, light transmission values for conventionally prepared nitrophe'nols have been in the range of 45 to 90 percent. Characteristically, the color of solid o-nitrophenol prepared from existing processes ranges from brown to orange. The product obtained in accordance with the method of the present invention is highly satisfactory in that light transmission values in excess of 95percent may be obtained, and color of the solid product varies from yellow to light yellow.

It is therefore an object of this invention to provide o-nitrophenol having improved color. More specifically, it'is an object of this invention to provide a simple, economical method of preparing o-nitrophenol having an improvedvalue of light transmission without resort to subsequent refining steps.

According to the present invention, addition to the alkaline reaction mass after hydrolysis of a color inhibitor selected from the group consisting of alkali metal bisulfites, alkali metal metabisulfites, urea and sulfur dioxide followed by normal acidification of the reaction mass to o-nitrophenol results in a final product having excellent color.

In a more specific embodiment of this invention, sodium o-nitrophenate or potassium o-nitrophenate is prepared according to existing processes by hydrolysis of o-nitrochlorobenzene with caustic soda or caustic potash. The alkaline reaction mass is then cooled for subsequent processing and thereafter small amounts of an alkali metal bisulfite, alkali metal metabisulfite, urea, or sulfur dioxide are added by appropriate means known by those skilled in the art. The amount of color inhibitor required is not critical and is limited only by economic considerations and operating convenience. Amounts of inhibitor from 0.1 to 5.0 percent by weight of the alkali metal o-nitrophenate in the reaction mass are effective in preparing o-nitrophenol having excellent color. Temperature of the alkaline reaction mass is not critical to effectiveness of the color inhibitor and those skilled in the art will recognize that process convenience is the major factor in selecting the temperature at which addition of the inhibitor is made. Good results are obtained at temperatures in the range of 50 to 100C. 7

Following addition of inhibitor, the reaction mass is acidified toa pH. in the range of 2 to 3 and the resulting o-nitrophenol is then separated from the acid layer.

The .following examples illustrate the advantageous and unexpected results achieved by the color inhibitors of this invention, but it is not intended that this invention be limited by or to the examples.

EXAMPLE 1 A 13 percent by weight slurry of sodium 0- nitrophenate in water is prepared conventionally by hydrolysis of o-nitrochlorobenzene with sodium hydroxide in an. autoclave, sparged with steam to remove excess o-nitrochlorobenzene and cooled t 50-60C for subsequent processing.

A 400 gram sample of the 13 percent sodium 0- nitrophenate slurry is then acidified with concentrated sulfuric acid in the conventional manner to Congo red endpoint (pH of 2.5-3) and the resulting o-nitrophenol separated from the acid layer. When solidified, the product color is orange. A 5 percent by weight solution of this onitrophenol is then prepared and light transmission measured with a Beckman Spectronic 20 instrument using a 1 inch cell at wavelengths of 475 millimicrons. Light transmission through the sample is 48 percent.

Another 400 gram sample of the 13 percent slurry prepared above is treated by the addition of 0.5 gram of sodium metabisulfite and then acidified in the manner just described. o-Nitrophenol is again separated from the acid layer, and light transmission measured as with the previous sample. Light transmission through the sample in which color body formation has been inhibited is 83 percent. Color of this solidified product is yellow.

EXAMPLE 2 Using the procedure described in Example 1, additional samples are prepared with the following results using, in this instance a light wavelength of 560 millimicrons:

Uninhibited sample percent light transmission,

orange color Inhibited sample 98 percent light transmission,

yellow color Similar results are obtained upon replacing the sodium metabisulfite in the foregoing examples with equivalent weights of potassium metabisulfite, sodium metabisulfite, sodium bisulfite, urea, or sulfur dioxide.

While this invention has been described with respect to certain embodiments, it is not so limited, and it is to be understood that variations and modifications thereof may be made which are obvious to those skilled in the art without departing from the spirit or scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a process for preparing o-nitrophenol having improved color by hydrolysis of o-nitrochlorobenzene 2. A process of claim 1 wherein the color inhibitor is an alkalimetal bisulfite.

3. A process of claim 1 wherein the color inhi itor is sodium bisulfite.

4. A process of claim 1 wherein the color inhibitor is an alkali metal metabisulfite.

5. A process of claim 1 wherein the color inhibitor is sodium metabisulfite. 

2. A process of claim 1 wherein the color inhibitor is an alkali metal bisulfite.
 3. A process of claim 1 wherein the color inhibitor is sodium bisulfite.
 4. A process of claim 1 wherein the color inhibitor is an alkali metal metabisulfite.
 5. A process of claim 1 wherein the color inhibitor is sodium metabisulfite. 